Single cardiomyocytes from papillary muscles show lower preload-dependent activation of force compared to cardiomyocytes from the left ventricular free wall

Efficient pumping of the healthy left ventricle (LV) requires heterogeneities in mechanical function of individual cardiomyocytes (CM). Deformation of sub-endocardial (Endo) tissue is greater than that of sub-epicardial (Epi) regions. Papillary muscles (PM), often considered to be part of Endo tissue, show lower beat-by-beat length variation than Epi (or Endo) regions, even though they contribute to the shift in atrio-ventricular valve plane, which is essential for LV pump function. Thus far, no comparative assessment of CM mechanics for PM and LV free wall has been published. Here, we investigate contractility and cytosolic calcium concentration ([Ca